Amurselite (IMA2024-062), (NH4)2[(UO2)5(SeO3)3O2(OH)2(H2O)]·8H2O, is a new mineral discovered at the Burro mine, Slick Rock district, San Miguel County, Colorado, USA. It was found in a secondary efflorescent assemblage on asphaltite in association with gypsum, natrozippeite, quartz, and a potentially new lithium-uranyl-selenite mineral. Amurselite occurs as yellow prisms or blades. The streak is pale yellow, the luster is vitreous, the Mohs hardness is about 2, the tenacity is brittle, the fracture is irregular or stepped and the cleavages are perfect on {100} and fair on {010}. The mineral fluoresces weak green in 405 nm illumination. It is optically biaxial (−) with α = 1.580(5), β = 1.720(5), γ = 1.725(5) (white light); 2V = 18(3)°; optical orientation: X ^ a ≈ 20°, Y ^ b ≈ 44°; pleochroism: X colorless, Y and Z yellow; X < Y ≈ Z. The calculated density is 4.178 g/cm3 for the empirical formula. Electron probe microanalysis provided the empirical formula (NH4)1.87Na0.07K0.06U6+5Se4+2.98O32H20.07. Amurselite is triclinic, space group Pforumla⁠, a = 8.598(3), b = 9.088(3), c = 11.071(4) Å, α = 83.644(7), β = 68.776(7), γ = 79.940(8)°, V = 792.9(4) Å3, and Z = 1. In the crystal structure (R1 = 0.0505 for 1210 I > 2σI reflections), UO7 and UO8 polyhedra link by sharing equatorial edges to form chains, which are cross-linked by SeO32− groups to form sheets. The interlayer region contains NH4 and H2O.

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